Searches for factors affecting the mammalian gastro-intestinal (GI) tract are motivated by need for diagnostic and therapeutic agents. A protein may remain part of the mucin layer, providing mechanical (e.g., lubricant or gel stabilizer) and chemical (e.g. against stomach acid, perhaps helping to maintain the mucus pH gradient and/or hydrophobic barrier) protection for the underlying tissues. The trefoil peptide family has been suggested to have such general cytoprotectant roles (see Sands and Podolsky, 1996). Alternatively, a cytokine-like activity could help restore damaged epithelia. A suggestion that the trefoil peptides may act in concert with other factors to maintain and repair the epithelium, further underlines the complexity of interactions that take place in the gastrointestinal tract (Podolsky, 1997). The maintenance of the integrity of the GI epithelium is essential to the continued well-being of a mammal, and wound closing after damage normally occurs very rapidly (Lacy, 1998), followed by proliferation and differentiation soon thereafter to reestablish epithelial integrity (Nursat et al., 1992). Thus protection and restitution are two critical features of the healthy gastrointestinal tract, and may be important in the relatively harsh extracellular environment of the stomach.
Searches for GI proteins have met with some success. Complementary DNA (cDNA) sequences to messenger RNAs (mRNA) isolated from human and porcine stomach cells were disclosed in the University of Chicago Ph.D. thesis “Characterization of a novel messenger RNA and immunochemical detection of its protein from porcine gastric mucosa,” December 1987, by one of the present inventors working with the other inventors. However, there were several cDNA sequencing errors that led to significant amino acid changes from the AMP-18 protein disclosed therein. The protein itself was isolated and purified only as an aspect of the present disclosure, and functional analyses were performed to determine utility. Nucleic acid coding sequences were sought.